U.S. Pat. No. 4,159,685 discloses a buttonhole stitching in an electronic control sewing machine, where amplitudes of left and right line tacks are adjusted while the maximum amplitude of the buttonhole stitchings is utilized, in order to control the cut width.
The cut width of the buttonhole is generally determined in dependence upon the thickness of a button, shrinkage of stitches due to the sort of a fabric to be sewn and other factors. If the cut width is changed, the width of each of the line tacks is made different, and the resulting shapes of the buttonholes are not appealing in aesthetic appearance.